1. Field of the Invention
The present invention relates generally to electromagnetic solenoid construction and, more particularly, to a solenoid with the capability of being easily adjustable to establish a predetermined armature force to account for variations in the solenoid construction due to manufacturing tolerances and supply voltage deviations.
2. Description of the Prior Art
Electromagnetic solenoids are well-known in the prior art for use in a variety of applications. In one form solenoids may be used in pressure surge fuel pumps which may be fitted with high pressure nozzles suitable for direct injection of fuel into a combustion chamber of an internal combustion engine. These pumps typically comprise an electromagnetic coil which serves to activate an armature which in turn may drive a plunger to create a high pressure fuel condition which opens a valve and causes a fuel spray to be discharged through a nozzle. An example of such a combined pump and nozzle assembly is disclosed in U.S. Pat. No. 5,630,401 to Binversie et al. and assigned to the common assignee herein.
It is important in the design and manufacture of an electromagnetic fuel injection pump for an internal combustion engine to construct such a device such that it delivers a precise amount of fuel to the associated combustion chamber so that a proper fuel-to-air ratio is achieved. Too much fuel can not only waste fuel but also cause undesirable emissions from the engine. Too little fuel can cause the engine to run with excessive heat build-up and damage the engine. With an electromagnetic fuel injection pump constructed by mass production techniques natural manufacturing tolerances can cause such pumps to vary in terms of pumping pressure and fuel discharge quantity. In addition, variations in electrical current to the pump can also cause consequent variations in fuel discharge quantity. Accordingly, it is desirable to provide an electromagnetic fuel injection pump which is readily manufacturable by known mass production techniques but is also adjustable such that it can be set to deliver a precise predetermined amount of fuel despite the occurrence of normal manufacturing tolerances. It is further desirable to provide such a pump which is easily adjusted to account for variations in electrical operating current.